Aminoguanidine bicarbonate (AGB) is of practical importance because of its use in dyes, dispersants, explosives and other commercial applications.
Processes for the production of AGB may be divided into three groups:
1. Reduction of nitroguanidine or nitrosoguanidine; PA1 2. The hydrazinolysis of nitrosoguanidine or S-alkylisothiourea; and PA1 3. The hydrazination of cyanamide.
The last of these three methods is commercially the most interesting as far as the production of AGB on a large scale is concerned. This process utilizes an aqueous cyanamide, a sodium cyanamide or a calcium cyanamide reacted with hydrazine. The hydrazination process utilizing calcium cyanamide is preferred.
U.S. Pat. No. 3,673,253 to Simons describes a process for producing aminoguanidine bicarbonate in which a calcium cyanamide is reacted with hydrazine in an aqueous medium at a pH of 7 to 9.5. The lowest cyanamide concentration possible must be maintained throughout the reaction as long as the hydrazine concentration is more than about 10 to 30 percent of the initial concentration. This is to prevent formation of dicyandiamide which does not react with hydrazine to produce aminoguanidine in good yields. Sulfuric acid is utilized to adjust the pH. The resulting aminoguanidine solution is treated with a bicarbonate precipitating agent to precipitate the AGB (column 2, lines 4-60). However, the presence of iron contaminants result in this AGB product being yellow in color which is unacceptable, especially if further processing into triazoles, azo dyes, sensitizers and the like is desired. To obtain AGB which is white in color, an additional processing step to remove the iron contaminants from the solution must be performed before addition of the precipitating agent. Alternatively, the iron contaminates are precipitated out with the calcium sulfate thus contaminating the calcium sulfate (column 3, line 53 - column 4, line 44). Each additional step is time-consuming and costly. Also, contamination of the calcium sulfate is undesirable. According to Simons, the reaction of calcium cyanamide with hydrazine in an acid medium having a pH of from 5 to 6 produces unacceptable laboratory yields of only 45 to 65 percent. In large scale batches, the yield is further reduced because the calcium sulfate "sludge" is almost impossible to wash out (column 1, lines 66-73).
An object of the present invention is to provide a process for producing relatively pure AGB in relatively high yields from calcium cyanamide, hydrazine hydrate and a bicarbonate which eliminates specific steps to remove contaminants present in the starting materials and contamination of precipitates of the process by these contaminants.